Single cell suspensions were prepared from normal rat and from the R 3230 AC mammary tumor propagated in the Fischer rat. Plasma membranes prepared by a variety of methods from the normal and cancerous cells showed difference in their carbohydrate composition and their protein patterns on SDS gel electrophoresis. The rate of aggregation of the isolated cells was determined (about 50-70 percent in 12 hours) and the effects of serum and other proteins showed that the rate was decreased. Studies on the synthesis of lactose and alpha-lactalbumin in the cell suspensions are under progress. Other studies have indicated that mammary tissue preparations will bind prolactin and further studies are in progress.